Polymers of vinyl chloride suitable for processing into high-durometer type products must exhibit satisfactory pouring properties, which are produced by a coarse, uniform grain. In general, particle distribution required for high-durometer processing is more than 90% larger than 63.mu. and less than 50% larger than 160.mu.. Other desirable properties of polymers intended for hard or high-durometer processing are high thermal stability as well as ability to slip and move easily within the extruder.
Polymers of vinyl chloride suitable for hard processing have been made in the presence of alkali salts of fatty acids as emulsifiers. The polymerization is conducted in an alkaline medium because alkali metal salts of fatty acids have pH values of at least 9.5 in an aqueous medium, and thus are fully effective as emulsifiers only at these pH values.
Polymers obtained by polymerization in the presence of alkali salts of fatty acids as emulsifiers have considerably higher thermal stability than polymers obtained by polymerization in the presence of alkyl sulfates, alkyl and alkylaryl sulfonates and other customary emulsifiers (cf. Table 2). Polymers produced by prior art processes with alkali salts of fatty acids as emulsifiers, however, have an unsatisfactory, slightly yellow inherent color.
It is an object of the present invention to improve the inherent color of vinyl chloride polymers manufactured with alkali metal salts of fatty acids as emulsifiers.